Methods for the treatment of a flue gas stream using sorbent compositions having amorphous halogen species

ABSTRACT

Methods for the manufacture of sorbent compositions, sorbent compositions and methods for using the sorbent compositions. The methods include the utilization of an acidic halogen solution as a source of a halogen species that is dispersed on a solid sorbent. The use of the acidic halogen solution results in a highly active halogen species that demonstrates improved efficacy for the removal of heavy metal(s) from a flue gas. The sorbent composition includes a substantially amorphous halogen species associated with a solid sorbent such as powdered activated carbon (PAC).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit as a divisional applicationof co-pending U.S. patent application Ser. No. 15/237,089 filed on Aug.15, 2016, which claims the benefit as a continuation-in-part applicationof U.S. patent application Ser. No. 14/826,872 filed on Aug. 14, 2015.Each of these applications is incorporated herein by reference in itsentirety.

FIELD

This disclosure relates to the field of sorbent compositions for thesequestration of contaminants from a fluid, such as for thesequestration of heavy metals from a flue gas stream.

BACKGROUND

Stricter regulations for the reduction of mercury emissions from, e.g.,coal fired boilers necessitate the development of improved sorbentmaterials to sequester mercury and remove it from discharge streams toat least the level required to meet regulatory limits. One such sorbentmaterial is based on powdered activated carbon (PAC), and there is aneed to improve the ability of the sorbent to affect higher levels ofmercury capture from flue gas streams. The injection of halogens withthe coal or the addition of halogen salts such as halide salts to thesurface of a sorbent has been demonstrated to enhance mercury capture inthis regard.

Thus, the use of a halogen in sorbent compositions is a leadingtechnology used to oxidize mercury to a form that can be captured, suchas is disclosed in U. S. Pat. No. 9,539,538 to Wong et al., which isincorporated herein by reference in its entirety. In some cases, thesorbent compositions include 10 wt. % or more of the halogen. In somecases the halogen is added separately from the sorbent, as in U.S. Pat.No. 8,309,046 to Pollack et al. which is also incorporated herein byreference in its entirety.

SUMMARY

The addition of a halogen salt for the sequestration of mercury, e.g.,adding a halide salt to the sorbent composition, presumably enhances theoxidation of elemental gas phase mercury to a cationic species that ismore strongly sequestered in the pores of the sorbent. It is believed,however, that the degree of mercury oxidation and sequestration islimited by the reactivity of the halogen salts. It is believed thathalogen salt reactivity towards mercury oxidation may be limited byvarious aspects of the salt such as composition, crystallitesize/surface area, volatility, location within the sorbent pore network,poisoning from flue gas constituents such as acid gases (e.g., SO₃ andNO₂) and/or the bonding strength of the active halogen moiety to thesorbent surface.

It has been found that the use of an amorphous (e.g., non-crystalline)halogen in association with a solid sorbent yields a unique sorbentcomposition that demonstrates enhanced heavy metal removal from a fluegas stream compared to the same base sorbent treated with a halide saltin substantially crystalline form. In particular, it has been found thatutilizing an acidic halogen solution that includes a halogen species andan acid to form the sorbent composition results in significantlyimproved sequestration of heavy metals (e.g., mercury) as compared to asimilar sorbent composition that is prepared using conventional methods.This approach is believed to be effective for a wide range of acids,halide salts, and sorbents.

In one embodiment, a method for the manufacture of a sorbent compositionis disclosed. The method includes the step of contacting a solid sorbentwith an acidic halogen solution, the acidic halogen solution comprisingan acid and a halogen species derived from a halide salt. The contactingstep forms a sorbent composition comprising the solid sorbent and thehalogen species.

A number of characterizations, refinements and additional features areapplicable to this embodiment of a method for the manufacture of asorbent composition. These characterizations, refinements and additionalfeatures are applicable to this embodiment of a method for themanufacture of a sorbent composition individually or in any combination.

In one characterization, the acidic halogen solution comprises a mineralacid. For example, the mineral acid may be selected from the groupconsisting of sulfuric acid, phosphoric acid, nitric acid, hydrochloricacid and combinations thereof. In one particular characterization, themineral acid comprises sulfuric acid. In another particularcharacterization, the mineral acid comprises phosphoric acid.

In another characterization, the halogen species comprises a halogenthat is selected from the group consisting of bromine, chlorine, iodineand combinations thereof. In a further characterization, the halide saltcomprises a halogen anion and a cation selected from the groupconsisting of lithium, sodium, potassium, calcium, magnesium, ammonium,alkyl ammonium, hydrogen and combinations thereof. For example, thehalogen species may comprise bromine, and the halide salt may beselected from the group consisting of sodium bromide, ammonium bromideand combinations thereof.

The solid sorbent may be selected from the group consisting of silica,silicates, carbonaceous materials, and combinations thereof. In certaincharacterizations, the solid sorbent comprises a carbonaceous material.In a further refinement of this characterization, the carbonaceousmaterial is derived from coal, and may be derived from lignite coal. Inone refinement, the solid sorbent comprises powdered activated carbon.

In certain characterizations, it is desirable that the median averageparticle size (D50) of the sorbent composition (e.g., of the solidsorbent) is relatively small. In one characterization, the solid sorbenthas a median average particle size (D50) of not greater than about 25μm. In another characterization, the solid sorbent has a relatively hightotal pore volume. In one characterization, the solid sorbent has atotal pore volume of at least about 0.2 cc/g. In anothercharacterization, the solid sorbent has a relatively high total surfacearea. In one characterization, the solid sorbent has a surface area ofat least about 350 m²/g.

The step of contacting the solid sorbent with the acidic halogensolution may be carried out using a number of techniques. In onecharacterization, the method includes the step of forming the acidichalogen solution comprising the halogen species before contacting thesolid sorbent with the acidic halogen solution. In one characterization,the step of forming the acidic halogen solution comprises dissolving thehalide salt in an aqueous solvent to form an aqueous halide saltsolution, and thereafter combining the acid with the aqueous halide saltsolution. In one characterization, the contacting step includes sprayingthe acidic halogen solution onto the solid sorbent. In any event, themolar ratio of halogen species to acid in the acidic halogen solutionmay be not greater than about 10:1, such as not greater than about 8:1,such as not greater than about 5:1, or even not greater than about 2:1.In another characterization, the molar ratio of halogen species to acidin the acidic halogen solution is at least about 1:2.

In a further characterization, the step of contacting the solid sorbentwith the acidic halogen solution includes the steps of dispersing thehalide salt onto the solid sorbent, and thereafter contacting the halidesalt and the solid sorbent with the acid to form the acidic halogensolution comprising the acid and the halogen species on the solidsorbent. In one refinement, the step of dispersing the halide salt ontothe solid sorbent includes admixing dry particulates of the halide saltwith the solid sorbent. In another refinement, the step of dispersingthe halide salt onto the solid sorbent comprises contacting asubstantially non-acidic halogen solution of the halide salt with thesolid sorbent.

In another characterization, the step of contacting the solid sorbentwith the acidic halogen solution includes the steps of contacting thesolid sorbent with the acid to form an acid-treated solid sorbent anddispersing the halide salt onto the acid-treated solid sorbent to formthe acidic halogen solution. In one refinement, the step of dispersingthe halide salt onto the acid-treated solid sorbent comprises admixingdry particulates of the halide salt with the acid-treated solid sorbent.In another refinement, the step of dispersing the halide salt onto theacid-treated solid sorbent comprises contacting a substantiallynon-acidic halogen solution of the halide salt with the acid-treatedsolid sorbent.

In another characterization, the method further includes the step ofadding at least a second halide salt to the solid sorbent.

In another characterization, the sorbent composition includes notgreater than about 30 wt. % of the halogen species. In yet anothercharacterization, the sorbent composition includes at least about 0.5wt. % of the halogen species.

In another characterization, the method further includes the step ofadding an acid gas agent to the sorbent composition. In anothercharacterization, the method further includes the step of adding a flowaid to the sorbent composition.

In another embodiment, a sorbent composition is disclosed. The sorbentcomposition includes a solid sorbent and a halogen species associatedwith the solid sorbent, wherein the halogen species is in asubstantially amorphous form on the solid sorbent.

A number of characterizations, refinements and additional features areapplicable to this embodiment of a sorbent composition. Thesecharacterizations, refinements and additional features are applicable tothis embodiment of a sorbent composition individually or in anycombination.

In one characterization, the sorbent composition is formed by the methoddescribed above. For example, the halogen species may be derived bycontacting at least a first halide salt with an acid. In one refinement,the halogen species associated with the solid sorbent is dispersedwithin the acid. In another refinement, the acid is a mineral acid, suchas a mineral acid selected from the group consisting of sulfuric acid,phosphoric acid, nitric acid, hydrochloric acid and combinationsthereof. In yet a further refinement, the sorbent composition comprisesa conjugate salt of the mineral acid. In yet a further refinement, thesorbent composition comprises an anion selected from the groupconsisting of sulfate, bisulfate, phosphate, hydrogen phosphate,dihydrogen phosphate, nitrate, chloride anions, and combinationsthereof. For example, the mineral acid may comprise sulfuric acid, andthe sorbent composition may comprise a polyatomic anion selected fromthe group consisting of sulfate, bisulfate and combinations thereof. Inanother example, the mineral acid comprises phosphoric acid and thesorbent composition comprises a polyatomic anion selected from the groupconsisting of phosphate, hydrogen phosphate, dihydrogen phosphate andcombinations thereof.

In another characterization, the halogen species is selected from thegroup consisting of bromine, chlorine, iodine and combinations thereof.For example, in one characterization, when the halogen species isderived by contacting at least a first halide salt with an acid, thefirst halide salt comprises a halogen anion and a cation selected fromthe group consisting of lithium, sodium, potassium, calcium, magnesium,ammonium, alkyl ammonium, hydrogen and combinations thereof.

In another characterization, the halogen species comprises bromine. Forexample, when the halogen species is derived by contacting at least afirst halide salt with an acid, the first halide salt may be selectedfrom the group consisting of sodium bromide, ammonium bromide andcombinations thereof.

In another characterization, the sorbent composition comprises at leastabout 0.5 wt. % of the halogen species. In one refinement, the sorbentcomposition comprises at least about 5 wt. % of the halogen species. Inanother characterization, the sorbent composition comprises not greaterthan about 30 wt. % of the halogen species, and in one refinement thesorbent composition comprises not greater than about 15 wt. % of thehalogen species.

In another characterization, the sorbent composition comprises at leastabout 3 wt. % moisture, and in one refinement the sorbent compositioncomprises at least about 8 wt. % moisture. In another characterization,the sorbent composition comprises not greater than about 15 wt. %moisture.

In another characterization of the sorbent composition, the solidsorbent is selected from the group consisting of alumina, silica,silicates, carbonaceous materials, and combinations thereof. In onerefinement, the solid sorbent comprises a carbonaceous material, forexample wherein the carbonaceous material is derived from coal. In oneparticular refinement, the carbonaceous material is derived from lignitecoal. In another refinement, the solid sorbent comprises powderedactivated carbon.

In a further characterization of the sorbent composition, the solidsorbent has a median average particle size (D50) of not greater thanabout 30 μm, and in a further refinement of this characterization thesolid sorbent has a median average particle size of not greater thanabout 15 μm. In another characterization of the sorbent composition, thesolid sorbent has a total pore volume of at least about 0.2 cc/g. Inanother characterization of the sorbent composition, the solid sorbenthas a surface area of at least about 350 m²/g.

In yet another characterization, the sorbent composition furthercomprises at least a second halogen species associated with the solidsorbent. In yet a further characterization, the sorbent compositionfurther comprises an acid gas agent. For example, the acid gas agent maybe selected from the group consisting of aluminum hydroxide, zinc oxide,ammonium sulfate, ammonium bisulfate, ammonium carbonate, ammoniumbicarbonate, sodium carbonate, sodium bicarbonate, magnesium hydroxide,magnesium carbonate, magnesium bicarbonate, urea, urea derivatives,metal hydroxides, ammonium compounds, and combinations thereof. In oneparticular characterization, the acid gas agent comprises aluminumhydroxide. In one refinement, the sorbent composition comprises at leastabout 1 wt. % of the acid gas agent and not greater than about 20 wt. %of the acid gas agent.

In another characterization, the sorbent composition further comprises aflow aid. In one refinement, the flow aid is selected from the groupconsisting of graphite, mica, talc, silica, stearates, clays,diatomaceous earth and combinations thereof. In one particularrefinement, the flow aid comprises graphite. In another particularrefinement, the flow aid comprises mica.

In another embodiment, a method for the treatment of a flue gas streamto remove contaminants from the flue gas stream is disclosed. The methodmay include combusting a fuel, the combusting of the fuel generating aflue gas stream comprising at least one contaminant contained in theflue gas stream. The flue gas stream is contacted with a solid sorbentcomposition, wherein the contacting oxidizes at least a portion of theat least one contaminant to form an oxidized contaminant. After thecontacting step, the solid sorbent composition is separated from theflue gas stream. The solid sorbent composition a comprises solid sorbentand a halogen species associated with the solid sorbent, wherein thehalogen species is in a substantially amorphous form on the solidsorbent, and wherein the solid sorbent sequesters the oxidizedcontaminant.

A number of characterizations, refinements and additional features areapplicable to this embodiment of a method for the treatment of a fluegas stream to remove contaminants from the flue gas stream. Thesecharacterizations, refinements and additional features are applicable tothis embodiment of a method for treatment of a flue gas stream to removecontaminants from the flue gas stream individually or in anycombination.

In one characterization, the halogen species is formed by contacting atleast a first halide salt with an acid. In one refinement, the halogenspecies associated with the solid sorbent is dispersed within the acid.The acid may be a mineral acid, such as a mineral acid selected from thegroup consisting of sulfuric acid, phosphoric acid, nitric acid,hydrochloric acid and combinations thereof. In this regard, the sorbentcomposition may include a conjugate salt of the mineral acid. In anothercharacterization, the sorbent composition comprises an anion selectedfrom the group consisting of sulfate, bisulfate, phosphate, hydrogenphosphate, dihydrogen phosphate, nitrate, chloride, and combinationsthereof. In one particular refinement, the mineral acid comprisessulfuric acid. In this refinement, the sorbent composition may include apolyatomic anion selected from the group consisting of sulfate,bisulfate and combinations thereof. In another characterization, themineral acid comprises phosphoric acid. In this refinement, the sorbentcomposition may include a polyatomic anion selected from the groupconsisting of phosphate, hydrogen phosphate, dihydrogen phosphate andcombinations thereof.

In another characterization of the method for the treatment of a fluegas stream to remove contaminants from the flue gas stream, the halogenspecies is selected from the group consisting of bromine, chlorine,iodine and combinations thereof. When the halogen species is formed bycontacting at least a first halide salt with an acid, the first halidesalt may include a halogen anion and a cation selected from the groupconsisting of lithium, sodium, potassium, calcium, magnesium, ammonium,alkyl ammonium, hydrogen and combinations thereof.

In another characterization, the halogen species comprises bromine. Whenthe halogen species is formed by contacting at least a first halide saltwith an acid, the first halide salt may be selected from the groupconsisting of sodium bromide, ammonium bromide and combinations thereof.

In another characterization, the sorbent composition comprises at leastabout 0.5 wt. % of the halogen species, and in one particular refinementthe sorbent composition comprises at least about 5 wt. % of the halogenspecies. In another characterization, the sorbent composition comprisesnot greater than about 30 wt. % of the halogen species, an in oneparticular refinement the sorbent composition includes not greater thanabout 15 wt. % of the halogen species.

In another characterization of the method for the treatment of a fluegas stream to remove contaminants from the flue gas stream, the sorbentcomposition comprises at least about 3 wt. % moisture, and in oneparticular refinement the sorbent composition comprises at least about 8wt. % moisture. In another characterization, the sorbent compositioncomprises not greater than about 15 wt. % moisture.

In another characterization of the method for the treatment of a fluegas stream to remove contaminants from the flue gas stream, the solidsorbent is selected from the group consisting of alumina, silica,silicates, carbonaceous materials, and combinations thereof. In oneparticular refinement, the solid sorbent comprises a carbonaceousmaterial. In another particular refinement, the carbonaceous material isderived from coal, for example from lignite coal. In one refinement, thesolid sorbent includes powdered activated carbon.

In a further characterization of the method for the treatment of a fluegas stream to remove contaminants from the flue gas stream, the solidsorbent has a median average particle size of not greater than about 30μm, and in a further refinement of this characterization the solidsorbent has a median average particle size of not greater than about 15μm. In another characterization of the sorbent composition, the solidsorbent has a total pore volume of at least about 0.2 cc/g. In anothercharacterization of the sorbent composition, the solid sorbent has asurface area of at least about 350 m²/g.

In yet another characterization, the sorbent composition furthercomprises at least a second halogen species associated with the solidsorbent. In yet a further characterization, the sorbent compositionfurther comprises an acid gas agent. For example, the acid gas agent maybe selected from the group consisting of aluminum hydroxide, zinc oxide,ammonium sulfate, ammonium bisulfate, ammonium carbonate, ammoniumbicarbonate, sodium carbonate, sodium bicarbonate, magnesium hydroxide,magnesium carbonate, magnesium bicarbonate, urea, urea derivatives,metal hydroxides, ammonium compounds, and combinations thereof. In oneparticular characterization, the acid gas agent comprises aluminumhydroxide. In one refinement, the sorbent composition comprises at leastabout 1 wt. % of the acid gas agent and not greater than about 20 wt. %of the acid gas agent.

In another characterization, the sorbent composition further comprises aflow aid. In one refinement, the flow aid is selected from the groupconsisting of graphite, mica, talc, silica, stearates, clays,diatomaceous earth and combinations thereof. In one particularrefinement, the flow aid comprises graphite. In another particularrefinement, the flow aid comprises mica.

In yet another refinement, the at least one contaminant is mercury.

Additional embodiments, as well as characterizations and refinements ofthese embodiments will be apparent to those of ordinary skill in the artupon review of the following description and the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic of a flue gas train and method for thetreatment of a flue gas for the removal of contaminants according to oneembodiment of this disclosure.

FIG. 2 illustrates x-ray diffraction patterns for a conventional sorbentcomposition and a sorbent composition according to the presentdisclosure.

FIG. 3 is a data plot illustrating the efficacy of certain sorbentcompositions disclosed herein for the removal of mercury from a flue gasstream.

DETAILED DESCRIPTION

In one embodiment, a method for the manufacture of a sorbent compositionis disclosed. The method may include the step of contacting a solidsorbent with an acidic halogen solution, where the acidic halogensolution includes an acid and a halogen species derived from a halidesalt, to form a sorbent composition that includes the solid sorbent andthe halogen species.

It is generally known that a halogen (e.g., bromine) facilitates theoxidation of mercury during the capture and sequestration of mercury bya sorbent (e.g., powdered activated carbon). However, halogens may havesome detrimental effects on the processing equipment. Therefore, it isdesirable to obtain the oxidation benefits of the halogen while using aslittle of the halogen as reasonably possible.

It has unexpectedly been found that when the halogen species is derivedfrom a halide salt and the halogen species is in the presence of anacid, the oxidation performance of the halogen species is increased. Thehalogen species in the presence of an acid is sometimes referred toherein as an acid activated halogen species, it being understood thatthe term “acid activated” does not refer to any specific mechanism ortheory behind the increased oxidation performance of the halogenspecies.

Numerous acids may be utilized in accordance with the foregoing method.The acid may be an organic acid or an inorganic acid. When an organicacid is employed, the organic acid should be a relatively strong acid(i.e., with a relatively low acid dissociation constant), such as pKa<2,e.g., oxalic acid (pK_(a)=1.2). Although organic acids may be useful, itis believed to be more desirable to use a mineral acid (i.e., aninorganic acid) as the acid, and a wide variety of mineral acids may beuseful in the present method. For example, the mineral acid may beselected from, but is not limited to, the group consisting of sulfuricacid (H₂SO₄), phosphoric acid (H₃PO₄), nitric acid (HNO₃), hydrochloricacid (HCl), as well as mixtures of these acids and other mineral acids.Particularly useful acids for this method include sulfuric acid andphosphoric acid. In one particular characterization, the acid comprisesphosphoric acid.

A variety of halogens may be used in this method. For example, thehalogen species may include a halogen that is selected from, but is notlimited to, the group consisting of bromine, chlorine and iodine,including combinations thereof. In one characterization, bromine may beparticularly effective as the halogen. In another characterization,iodine is utilized as the halogen. Among the possible combinations, itmay be particularly effective to utilize both bromine and iodine as thehalogens. The term halogen species includes simple ionic forms of theseelements (e.g., halide salts) as well as complex forms of the halogensuch as oxyanion salts (e.g., bromate).

As is noted above, the acid activated halogen species is derived from ahalogen salt, e.g. from a compound that includes a halogen anion and acation. The cation may be a single element, e.g., where the cation isselected from the group consisting of lithium, sodium, potassium,calcium, magnesium, hydrogen and combinations of these cations. Thecation may also be a complex cation, such as where the cation comprisesammonium or alkyl ammonium. In one particular characterization, the acidactivated halogen species comprises bromine, and the halide salt isselected from the group consisting of sodium bromide (NaBr) and ammoniumbromide (NH₄Br), and combinations of the two. In another particularcharacterization, the acid activated halogen species comprises iodine,and the halide salt comprises potassium iodide (KI).

The solid sorbent may be selected from the group consisting of silica,silicates and carbonaceous materials, and combinations of these sorbentmaterials. In a particular embodiment, the solid sorbent comprises acarbonaceous material. For example, the carbonaceous material may bederived from coal, and in particular may be derived from lignite coal.In another characterization, the solid sorbent may comprise powderedactivated carbon (PAC). The PAC may be formed from a variety of carbonsources such as wood, coconut shells and the like. In one particularembodiment, the solid sorbent comprises PAC that has been derived fromcoal. PAC derived from coal may have many advantageous morphologicalproperties, such as high surface area, high overall porosity anddesirable pore size characteristics that are advantageous for thesequestration of mercury.

The median average particle size (D50) of the solid sorbent may berelatively small, particularly when the sorbent composition isengineered for the capture of mercury or other heavy metal contaminantsfrom a flue gas stream. In one characterization, the median averageparticle size of the solid sorbent is not greater than about 50 μm, suchas not greater than about 30 μm, or even not greater than about 25 μm.Particularly for the sequestration of mercury from a flue gas stream, itmay be desirable to utilize a solid sorbent having a median averageparticle size of not greater than about 20 μm, not greater than about 15μm and even not greater than about 12 μm. Characterized in another way,the median particle size may be at least about 5 μm, such as at leastabout 6 μm, or even at least about 8 μm. The D50 median average particlesize may be measured using techniques such as light scatteringtechniques (e.g., using a Saturn DigiSizer II, available fromMicromeritics Instrument Corporation, Norcross, Ga.).

In one characterization, the solid sorbent (e.g., PAC) has a relativelyhigh total pore volume and a well-controlled distribution of pores,particularly among the mesopores (i.e., from 20 Å to 500 Å width) andthe micropores (i.e., not greater than 20 Å width). A well-controlleddistribution of micropores and mesopores is desirable for effectiveremoval of mercury from the flue gas stream. While not wishing to bebound by any theory, it is believed that the mesopores are thepredominant structures for capture and transport of the oxidized mercuryspecies to the micropores, whereas micropores are the predominatestructures for sequestration of the oxidized mercury species.

In this regard, the total pore volume of the solid sorbent (sum ofmicropore volume plus mesopore volume plus macropore volume) may be atleast about 0.10 cc/g, such as at least 0.20 cc/g, at least about 0.25cc/g or even at least about 0.30 cc/g. The micropore volume of thesorbent may be at least about 0.10 cc/g, such as at least about 0.15cc/g. Further, the mesopore volume of the sorbent may be at least about0.10 cc/g, such as at least about 0.15 cc/g. In one characterization,the ratio of micropore volume to mesopore volume may be at least about0.7, such as 0.9, and may be not greater than about 1.5. Such levels ofmicropore volume relative to mesopore volume may advantageously enableefficient capture and sequestration of oxidized mercury species by thesolid sorbent. Pore volumes may be measured using gas adsorptiontechniques (e.g., N₂ adsorption) using instruments such as a TriStar IISurface Area Analyzer 3020 or ASAP 2020 (Micromeritics InstrumentsCorporation, Norcross, Ga., USA).

In another characterization, the solid sorbent has a relatively highsurface area. For example, the solid sorbent may have a surface area ofat least about 350 m²/g, such as at least about 400 m²/g or even atleast about 500 m²/g. Surface area may be calculated using theBrunauer-Emmett-Teller (BET) theory that models the physical adsorptionof a monolayer of nitrogen gas molecules on a solid surface and servesas the basis for an analysis technique for the measurement of thespecific surface area of a material. BET surface area may be measuredusing the Micromeritics TriStar II 3020 or ASAP 2020 (MicromeriticsInstrument Corporation, Norcross, Ga.).

In accordance with this method for the manufacture of a sorbentcomposition, the acidic halogen solution, which includes an acid and ahalogen species, is contacted with the solid sorbent to form the sorbentcomposition. The acidic halogen solution may be contacted with the solidsorbent in a variety of ways. For example, the acidic halogen solutionmay be formed before contact with the solid sorbent, or the acidichalogen solution may be formed on the solid sorbent, e.g., by theseparate addition of the acid and the halogen species to the sorbent.

Thus, in one characterization, the acidic halogen solution comprisingthe halogen species is formed before the step of contacting the acidichalogen solution with the sorbent. In one characterization, the step offorming the acidic halogen solution comprises dissolving the halide saltin an aqueous solvent (e.g., water) to form an aqueous halide saltsolution, and thereafter combining the acid with the halide saltsolution to form the acidic halogen solution. Alternatively, a barrenacidic solution (i.e., an acidic solution that is substantially freefrom halogens) may first be formed, and then the halide salt may beadded to the barren acidic solution to form the acidic halogen solutioncomprising the halogen species.

The thus-formed acidic halogen solution may be contacted with thesorbent, e.g., to coat the sorbent with the acidic halogen solution anddisperse the halogen species onto the sorbent. For example, the sorbentmay be immersed in the acidic halogen solution for a period of time andthen separated from the solution, or the acidic halogen solution may besprayed onto the sorbent. It is believed to be beneficial to control therelative amounts of acid and halogen species in the acidic halogensolution. For example, the molar ratio of halogen species to acid in theacidic halogen solution may be not greater than about 10:1, such as notgreater than about 8:1, not greater than about 5:1, or even not greaterthan about 2:1. However, the molar ratio of halogen species to acid inthe acidic halogen solution may be at least about 1:2.

In another embodiment, the step of contacting the solid sorbent with theacidic halogen solution may include dispersing the halide salt onto thesolid sorbent, and then contacting the halide salt and the solid sorbentwith the acid (e.g., without a halogen species) to form, on the solidsorbent, the acidic halogen solution comprising the acid and the halogenspecies. For example, the halide salt may be dispersed onto the solidsorbent by admixing substantially dry particulates of the halide saltwith the solid sorbent. Alternatively, a solution of the halide salt,e.g., where the halide salt is wholly or partially solubilized in anaqueous solution, may be contacted with the solid sorbent to dispersethe halide salt onto the sorbent.

In another embodiment, the step of contacting the solid sorbent with theacidic halogen solution includes first contacting the solid sorbent withthe acid to form an acid-treated solid sorbent, and then dispersing thehalide salt onto the acid-treated solid sorbent to form, on the solidsorbent, the acidic halogen solution comprising the acid and the halogenspecies. In this embodiment, the step of dispersing the halide salt ontothe acid-treated solid sorbent may include admixing dry particulates ofthe halide salt with the acid-treated solid sorbent, or may includecontacting a solution (e.g., substantially non-acidic aqueous) of thehalide salt with the acid-treated solid sorbent.

Any of the foregoing approaches for contacting the solid sorbent withthe acidic halogen solution may be applied individually, or in anycombination. For example, an acidic halogen solution comprising ahalogen species may be contacted with a solid sorbent that already hassome concentration of a halide salt associated with the sorbent, e.g.,dispersed on the sorbent. In such an example, the halogen species in theacidic halogen solution may be the same as the halogen contained in thehalide salt, or may be a different halogen. In another example, themethod may also include adding at least a second halide salt to thesolid sorbent, e.g., before or after the acidic halogen solutioncomprising the halogen species is contacted with the solid sorbent. Inone embodiment, an acidic halogen solution is contacted with the sorbentto deposit a first halogen species onto the sorbent. Thereafter, asecond halogen species that is different than the first halogen speciesis contacted with the acid activated sorbent, where the second halogenspecies is solubilized in an acid, or is solubilized in a substantiallynon-acidic solution. In one example, a sorbent is contacted with anacidic halogen solution (e.g., a solution of sodium bromide inphosphoric acid) and thereafter the sorbent is contacted with a solutionof a second halogen species that is not acid activated (e.g., a solutionof potassium iodide in water).

In one refinement of the foregoing method, the method may include dryingof the sorbent composition, e.g., drying the sorbent composition aftercontacting the solid sorbent with the acidic halogen solution. Thisdrying step may be applied to reduce the moisture level to a desiredrange, for example. In one characterization, the drying step includesdrying the sorbent composition to achieve a moisture level of notgreater than about 8 wt. %.

In any event, it is an advantage of the methods and compositionsdisclosed herein that the sorbent compositions may have an adequateefficacy (e.g., for mercury removal from a flue gas stream) atrelatively low concentrations of the halogen species. Characterizedanother way, at the same concentration of halogen species, the sorbentcompositions disclosed herein may have an improved efficacy in relationto known sorbents, i.e., sorbents where the halide salt has not beenexposed to an acid. In one example, the method forms a sorbentcomposition that includes not greater than about 30 wt. % of the halogenspecies, such as not greater than about 20 wt. % of the halogen species,not greater than about 15 wt. % of the halogen species, and even notgreater than about 12 wt. % of the halogen species, such as not greaterthan about 10 wt. % of the halogen species. However, for mostapplications, the method will form a sorbent composition that includesat least about 0.5 wt. % of the halogen species, such as at least about1.0 wt. % of the halogen species, at least about 2.0 wt. % of thehalogen species, or even at least about 3.0 wt. % of the halogenspecies. In one embodiment, the halogen species includes iodine and thesorbent composition includes not greater than about 5 wt. % iodine, suchas not greater than about 4 wt. % iodine and even not greater than about3 wt. % iodine. It has been found that iodine, particularlyacid-activated iodine as disclosed herein, can have a high degree ofefficacy even in such low concentrations in the sorbent.

Because the type and nature of the halogen species may vary, it is alsouseful to consider the concentration of the halogen species in terms ofthe molar concentration of the halogen. In this regard, the method mayform a sorbent composition that includes not greater than about 0.375mol. % of the halogen species, such as not greater than about 0.250 mol.% of the halogen species, not greater than about 0.188 mol. % of thehalogen species, and even not greater than about 0.150 mol. % of thehalogen species, such as not greater than about 0.125 mol. % of thehalogen species. However, in most applications the sorbent compositionwill include at least about 0.00625 mol. % of the halogen species, suchas at least about 0.0125 mol. % of the halogen species, at least about0.025 mol. % of the halogen species, or even at least about 0.0375 mol.% of the halogen species.

The method may include the addition of other additives to the sorbentcomposition, e.g., to enhance other characteristics of the sorbentcomposition. For example, the method may include adding an acid gasagent to the sorbent composition. Alternatively, or in addition to anacid gas agent, a flow aid may be added to the sorbent composition. Inaddition, a catalytic component such as a catalytic metal may be addedto the sorbent composition. Such acid gas agents, flow aids andcatalytic components are discussed in more detail below.

The present disclosure is also directed to a sorbent composition that isparticularly useful for the sequestration of contaminants, e.g., heavymetals, from a fluid stream, particularly where the contaminant isoxidized by a halogen to facilitate its removal, e.g., in the removal ofmercury from a flue gas stream. The sorbent composition includes a solidsorbent and a halogen species that is associated with the solid sorbent,where the halogen species is in a substantially amorphous (e.g.,non-crystalline) form on the solid sorbent. Although the sorbentcompositions disclosed herein may be prepared by the foregoingmethodology, e.g., where the halogen species is formed by contactinghalide salt(s) with an acid, it is to be understood that the sorbentcompositions disclosed and claimed herein are not limited to thoseprepared by this specific method.

As used herein, the term amorphous refers to the fact that the halogenspecies has no clearly defined shape or form on the solid sorbent. Thisis in contrast to a halogen species that has a clearly defined form(e.g., morphology) on the solid sorbent, particularly a substantiallycrystalline form that can be readily detected using techniques such asX-Ray Diffraction (XRD). Thus, when the sorbent compositions accordingto the present disclosure are analyzed using XRD, the diffractionpattern does not show the relatively sharp diffraction peaks that arecharacteristic of a crystalline solid that includes the halogen. Forexample, if the halogen species is bromine and the bromine is derivedfrom sodium bromide, the XRD pattern will not contain the relativelysharp peaks that are associated with the presence of crystalline sodiumbromide.

As is discussed above, the sorbent composition may be prepared by themethods disclosed above. That is, the halogen species may be formed bycontacting one or more halide salts with an acid, e.g., with an acidicsolution. When the halogen species is formed by contacting the halidesalt with an acid, the halogen species may be dispersed within the acidwhen the halogen species is associated with the solid sorbent. Forexample, the halogen species may be dispersed within an acid that partlyor substantially completely coats the solid sorbent. As is discussedabove, the acid may be an organic acid or a mineral acid, and inparticular embodiments the acid is a mineral acid. The mineral acid maybe selected from the group consisting of sulfuric acid, phosphoric acid,nitric acid and hydrochloric acid, as well as combinations of theseacids. Among these, sulfuric acid and phosphoric acid may beparticularly useful.

Thus, the halogen species may be dispersed in combination with a mineralacid on the surface of the solid sorbent. When the halogen species isdispersed in combination with a mineral acid, the sorbent compositionmay also include a conjugate salt of the mineral acid, i.e., may includean anion contributed by the acid. Such anions contributed by the acidmay include polyatomic or monoatomic ions, for example sulfate (SO₄ ²⁻),bisulfate (HSO⁴⁻), phosphate (PO₄ ³⁻), hydrogen phosphate (HPO₄ ²⁻),dihydrogen phosphate (H₂ PO⁴⁻), nitrate (NO³⁻) and chloride (Cl⁻)anions. For example, when the mineral acid comprises sulfuric acid(H₂SO₄), the sorbent composition may include sulfate and/or bisulfateanions. In another example, when the mineral acid comprises phosphoricacid (H₃PO₄), the sorbent composition may include phosphate, hydrogenphosphate and/or dihydrogen phosphate anions.

The halogen species may include a halogen element such as fluorine,chlorine, bromine and/or iodine. In one example, the halogen species isselected from the group consisting of bromine, chlorine, iodine andcombinations thereof. Bromine may be particularly useful in the sorbentcompositions disclosed herein, such as for the oxidation of heavy metalcontaminants. In other examples, iodine may be particularly useful inthe sorbent composition, particularly in relatively low concentrations.As is noted above, the halogen species may be formed by contacting oneor more halide salts with an acid. Such halide salts will typicallycomprise a halogen anion and a cation. For example, the cation may beselected from lithium, sodium, potassium, calcium, magnesium, ammonium,alkyl ammonium, and/or hydrogen. As a result, these cations may also bepresent in the sorbent composition, i.e., on the solid sorbent. In oneparticular example, the halogen species includes bromine and the halogenspecies is derived from sodium bromide and/or ammonium bromide. Thus,when sodium bromide is utilized, the halogen species will comprisebromine and the sorbent composition will also include sodium. Whenammonium bromide is utilized, the halogen species will comprise bromineand the sorbent composition will also include ammonium. In anotherparticular embodiment, the halogen species includes iodine and thehalogen species is derived from potassium iodide.

As is discussed above, it is an advantage of the sorbent compositionsdisclosed herein that the compositions may have an adequate efficacy(e.g., for mercury removal from a flue gas stream) at relatively lowconcentrations of the halogen species. Characterized another way, at thesame concentration of halogen species, the sorbent compositionsdisclosed herein may have an improved efficacy in relation to knownsorbents, i.e., sorbents where the halide salt has not been exposed toan acid. In one example, the sorbent composition includes not greaterthan about 30 wt. % of the halogen species, such as not greater thanabout 20 wt. % of the halogen species, not greater than about 15 wt. %of the halogen species, and even not greater than about 12 wt. % of thehalogen species. However, in most applications the sorbent compositionwill include at least about 0.5 wt. % of the halogen species, such as atleast about 1.0 wt. % of the halogen species, at least about 2.0 wt. %of the halogen species, or even at least about 5.0 wt. % of the halogenspecies. As is noted above, when the halogen species includes iodine,the sorbent composition may advantageously include not greater thanabout 5 wt. % iodine, such as not greater than about 4 wt. % iodine andeven not greater than about 3 wt. % iodine.

Because the type and nature of the halogen species may vary, it is alsouseful to consider the concentration of the halogen species in terms ofthe molar concentration of the halogen. In this regard, the sorbentcomposition may include not greater than about 0.375 mol. % of thehalogen species, such as not greater than about 0.250 mol. % of thehalogen species, not greater than about 0.188 mol. % of the halogenspecies, and even not greater than about 0.150 mol. % of the halogenspecies, such as not greater than about 0.125 mol. % of the halogenspecies. However, in most applications the sorbent composition willinclude at least about 0.00625 mol. % of the halogen species, such as atleast about 0.0125 mol. % of the halogen species, at least about 0.025mol. % of the halogen species, or even at least about 0.0375 mol. % ofthe halogen species.

The sorbent composition may also include moisture (e.g., water) on thesurface of the solid sorbent. It is believed that some level of moistureis desirable to help solubilize the oxidized mercury and facilitate itstransport into the sorbent pores. In this regard, the moisture may beacidic (i.e., an acidic solution) when the halogen species is derived bycontacting a halide salt with an acid. In this regard, it may beadvantageous to ensure that the sorbent composition includes at leastabout 3 wt. % moisture, such as at least about 8 wt. % moisture.However, it is believed that moisture levels in excess of about 15 wt. %may be detrimental to overall sorbent behavior, such as flow of thesorbent composition during conveyance of the sorbent composition. Themoisture level may be controlled by utilizing a drying step after thesolid sorbent has been contacted with the acidic halogen solution fromwhich the halogen species is derived, and controlling the time and/ortemperature of the drying step.

The solid sorbent may be selected from known sorbents that are usefulfor the sequestration of contaminants from a fluid stream. Particularexamples of such solid sorbents that may be useful in accordance withthe present disclosure include alumina, silica, silicates andcarbonaceous materials. In particular embodiments, the solid sorbentincludes a carbonaceous material, such as a carbonaceous material thatis derived from coal. In one example, the carbonaceous material isderived from lignite coal, and in another particular example the solidsorbent includes powdered activated carbon.

As is discussed above, the median average particle size (D50) of thesolid sorbent may be relatively small, particularly when the sorbentcomposition is engineered for the capture of mercury or other heavymetal contaminants from a flue gas stream. In one characterization, themedian average particle size of the solid sorbent is not greater thanabout 50 μm, such as not greater than about 30 μm, or even not greaterthan about 25 μm. For some applications such as the sequestration ofmercury from a flue gas stream, it may be desirable to utilize a solidsorbent having a median average particle size of not greater than about20 μm, not greater than about 15 μm and even not greater than about 12μm. Characterized in another way, the median particle size may be atleast about 5 μm, such as at least about 6 μm, or even at least about 8μm. The increased surface area may result in many benefits, including,but not limited to, increased exposure of the mercury to the halogenspecies associated with the solid sorbent surface, increased areaavailable for reactions to occur, and thus overall improved reactionkinetics. Generally speaking, the presence of the halogen species willnot substantially alter the particle size of the solid sorbent, and themedian particle size of the solid sorbent may be considered asequivalent to the median particle size of the sorbent composition.

The solid sorbent (e.g., PAC) may also have a relatively high total porevolume and a well-controlled distribution of pores, particularly amongthe mesopores (i.e., from 20 Å to 500 Å width) and the micropores (i.e.,not greater than 20 Å width). A well-controlled distribution ofmicropores and mesopores is desirable for effective removal of mercuryfrom the flue gas stream. While not wishing to be bound by any theory,it is believed that the mesopores are the predominant structures forcapture and transport of the oxidized mercury species to the micropores,whereas micropores are the predominate structures for sequestration ofthe oxidized mercury species.

In this regard, the total pore volume of the solid sorbent (sum ofmicropore volume plus mesopore volume plus macropore volume) may be atleast about 0.10 cc/g, such as at least 0.20 cc/g, at least about 0.25cc/g or even at least about 0.30 cc/g. The micropore volume of thesorbent may be at least about 0.10 cc/g, such as at least about 0.15cc/g. Further, the mesopore volume of the sorbent may be at least about0.10 cc/g, such as at least about 0.15 cc/g. In one characterization,the ratio of micropore volume to mesopore volume may be at least about0.7, such as 0.9, and may be not greater than about 1.5. Such levels ofmicropore volume relative to mesopore volume may advantageously enableefficient capture and sequestration of oxidized mercury species by thesolid sorbent.

In another characterization, the solid sorbent has a relatively highsurface area. For example, the solid sorbent may have a surface area ofat least about 350 m²/g, such as at least about 400 m²/g or even atleast about 500 m²/g. Surface area may be calculated using theBrunauer-Emmett-Teller (BET) theory that models the physical adsorptionof a monolayer of nitrogen gas molecules on a solid surface and servesas the basis for an analysis technique for the measurement of thespecific surface area of a material.

In accordance with the foregoing, the sorbent composition includes atleast one halogen species that is associated with the solid sorbent,where the at least one halogen species is in a substantially amorphousform on the solid sorbent. In some examples, the sorbent compositionincludes more than one halogen species on the solid sorbent. Thus, thesorbent composition may include at least a second halogen species on thesolid sorbent in addition to a first halogen species that is insubstantially amorphous form. The second halogen species may also be ina substantially amorphous form, i.e., where the second halogen speciesis also derived from contacting a halide salt (e.g., a second halidesalt) containing the second halogen with an acid. In another example,the second halogen species exists in a crystalline or partiallycrystalline form on the solid sorbent. For example, a sorbentcomposition may be formed that includes a halogen species in asubstantially amorphous form on the solid sorbent as is discussed above.Thereafter, a second halogen species may be introduced to the sorbentcomposition, such as by dry admixing the sorbent composition with asecond halide salt. Thus, the sorbent composition will include theamorphous halogen species and will also include a second halogen speciesthat is in the form of the second halide salt.

The sorbent compositions disclosed herein may include other additives,e.g., additives for improving the efficacy of the sorbent compositionswhen applied in different operating conditions. Merely by way ofexample, the sorbent composition may also include an acid gas agent thatis selected to improve the efficacy of the sorbent composition in thepresence of acid gases, such as those that might be found in a flue gasstream emanating from a coal-fired boiler. For example, the acid gasagent may include one or more of aluminum hydroxide, zinc oxide,ammonium sulfate, ammonium bisulfate, ammonium carbonate, ammoniumbicarbonate, sodium carbonate, sodium bicarbonate, magnesium hydroxide,magnesium carbonate, magnesium bicarbonate, urea, urea derivatives,metal hydroxides, and ammonium compounds. In one particular example, thesorbent composition includes aluminum hydroxide as an acid gas agent.The sorbent composition may include, for example, at least about 1 wt. %of the acid gas agent and not greater than about 20 wt. % of the acidgas agent.

In another example, the sorbent composition also includes a flow aidthat is selected to improve the flowability of the sorbent composition,such as during the pneumatic transport of the sorbent composition.Exemplary flow aids include graphites, micas, talcs, silicas, stearates,clays and diatomaceous earth. In particular examples, the flow aidincludes graphite and/or mica.

In another example, the sorbent composition may include an ancillarycatalyst component comprising at least one constituent selected from thegroup consisting of a catalytic metal, a precursor to a catalytic metal,a catalytic metal compound, a precursor to a catalytic metal compoundand combinations thereof. For example, the catalyst component mayinclude a catalytic metal or a precursor to a catalytic metal, where thecatalytic metal is selected from the group consisting of Fe, Cu, Mn, Pd,Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, Ce, and combinations thereof. In oneparticular characterization, the catalytic metal may be selected fromthe group consisting of Fe, Cu, Mn, Zn and combinations thereof. Thecatalytic metal may be present in the sorbent composition in the rangeof from about 0.001 wt. % to about 20 wt. %.

Other additives to sorbent compositions that are known to those skilledin the art may be included within the sorbent compositions disclosedherein without departing from the scope of the present disclosure.

The sorbent compositions disclosed herein are particularly useful forthe treatment of a flue gas stream to remove contaminants from the fluegas stream. The sorbent compositions are particularly useful for thesequestration of mercury from a flue gas stream containing the mercury.Thus, the present disclosure also encompasses a method for the treatmentof a flue gas stream to remove contaminants from the flue gas stream bycontacting the flue gas stream with a solid sorbent composition such asthose disclosed herein.

For example, the method may include the combusting of a fuel, where thecombusting of the fuel generates a flue gas stream that includes atleast one contaminant contained in the flue gas stream. The flue gasstream is contacted with a solid sorbent composition, where the solidsorbent composition upon contacting the flue gas stream oxidizes atleast a portion of the contaminant to form an oxidized contaminant.After contacting the flue gas stream with the solid sorbent compositionthe solid sorbent composition is separated from the flue gas stream. Thesolid sorbent composition includes a solid sorbent and a halogen speciesassociated with the solid sorbent, where the halogen species is in asubstantially amorphous form on the solid sorbent, and wherein the solidsorbent sequesters the oxidized contaminant. In particular, the solidsorbent composition may be embodied by the solid sorbent compositionsdescribed in detail above.

By way of example, FIG. 1 schematically illustrates a flue gas train andmethod for removal of heavy metals such as mercury from a flue gasstream produced by a coal-burning power plant using activated carboninjection (ACI) to contact a sorbent composition with the flue gasstream. Coal 101 or other fuel source is introduced into a boiler 102and the combustion of the coal 101 produces a flue gas stream 103. Theflue gas stream 103 exits the boiler 102 and may then proceed through aflue gas train that includes an air heater unit (AH) 104 where thetemperature of the flue gas stream 103 is reduced and heat values withinthe overall system are conserved. The flue gas train may include aseparation unit 105 through which the flue gas stream 103 traverses toremove particulate matter from the flue gas. For example, the separationunit 105 may comprise an electrostatic precipitator (ESP) and/or afabric filter for the removal of particulate matter before the treatedflue gas exits out a stack 106. For example, a cold-side (i.e., afterthe air heater unit) electrostatic precipitator can be used, as isillustrated in FIG. 1. It will be appreciated by those skilled in theart that the flue gas train may include other devices not illustrated inFIG. 1, such as a selective catalytic reduction unit (SCR) and the like,and may have numerous other configurations.

To sequester and remove heavy metals from the flue gas, a sorbentcomposition as disclosed herein may be introduced (e.g., injected into)to the flue gas stream 103 either before 107A or after 107B the airheater unit 104, but before the separation unit 105 which will removethe solid sorbent composition from the flue gas.

While the separation unit 105 may be selected from a number of devices,including an ESP or a fabric filter bag house, the sorbent compositiondisclosed herein may be particularly useful for removing mercury fromthe flue gas stream 103 when an ESP is utilized as the separation unit105. For example, the separation unit 105 can be a cold-side ESP. WhileESP units generally have a lower capital cost than a fabric filter baghouse unit, fabric filter bag house units are often utilized to increasethe contact time between the sorbent composition and the flue gas streambecause the unit traps the sorbent composition and the flue gascontinues to pass through the sorbent composition on the filter untilthe filter is rapped to remove the sorbent and other trapped materials.Such resident times are often deemed necessary to adequately capturemercury from the flue gas stream with temperatures of less than about350° F. However, utilizing the sorbent compositions disclosed herein,which may provide rapid oxidation of the mercury species, even veryshort residence times (e.g., the contact times) between the flue gasstream and the sorbent composition may be sufficient to remove at leastabout 85% of the mercury from the flue gas, such as at least about 90%of the mercury from the flue gas. In this regard, the residence time ofthe sorbent composition in the flue gas stream may be not greater thanabout 5 seconds, such as not greater than about 3 seconds or even notgreater than about 1 second.

EXAMPLES Comparative Example 1

A first comparative sample (Comparative Sample A) is obtained forcomparison to the sorbent compositions disclosed herein. Sample A is acommercial sorbent that is sold under the mark FastPAC® by ADA CarbonSolutions, LLC Littleton, Colo. Sample A comprises a powdered activatedcarbon (PAC) that is derived from a lignite coal feedstock. Sample A hasa median particle size (D50) of about 15 μm, a fixed carbon content ofabout 50 wt. %, a mineral content of about 40 wt. %, and a total porevolume of at least about 0.25 cc/g.

Comparative Example 2

A second comparative sample (Comparative Sample B) is a brominated PACsorbent wherein the bromine is added to the PAC via impregnation usingan aqueous solution of sodium bromide (NaBr). Comparative Sample B isknown to be effective for mercury removal from a flue gas stream.Comparative Sample B is prepared by spraying a solution of sodiumbromide onto 50 g of Comparative Sample A over a period of about 5minutes while the PAC is fluidized in a mixing vessel. After a totalmixing period of about 5 minutes, the composition is dried at 150° C.until a moisture level of about 8 wt. % is attained. The bromineconcentration on Comparative Sample B is measured to be about 5.6 wt. %.

Comparative Example 3

A third comparative sample (Comparative Sample C) is a brominated PACsorbent where the bromine is added to the PAC via impregnation using anaqueous solution of ammonium bromide. Such a composition is known to beeffective for mercury removal from flue gas. Comparative Sample C isprepared by spraying a solution of ammonium bromide onto 50 g ofComparative Sample A over a period of about 5 minutes while the carbonis fluidized in a mixing vessel. The bromine concentration onComparative Sample C is measured to be about 5.1 wt. %.

Example 4

Sample D in accordance with the present disclosure is prepared in thefollowing manner. Sodium bromide is dissolved in deionized (DI) water toform a sodium bromide solution. Thereafter, 85 wt. % phosphoric acid(H₃PO₄) is slowly added to the sodium bromide solution with stirring.The resulting acidic halogen solution comprises 22.4 wt. % bromine andhas a phosphoric acid to sodium bromide molar ratio of about 1:1. About14 g of this acidic halogen solution is sprayed onto about 50 g ofComparative Sample A over a period of about 5 minutes while ComparativeSample A is fluidized in a mixing vessel. After a further 5 minutes ofmixing, the sorbent composition is dried at about 150° C. until amoisture level of about 8 wt. % is attained. The bromine concentrationon Sample D is measured to be about 5.3 wt. %.

Example 5

Sample E in accordance with the present disclosure is prepared in thefollowing manner. Ammonium bromide (NH₄Br) is dissolved in DI water toform an ammonium bromide solution. 85 wt. % phosphoric acid is slowlyadded to the ammonium bromide solution with stirring. The resultingacidic halogen solution contains about 21.1 wt. % Br and has aphosphoric acid to ammonium bromide molar ratio of about 1:1.Thereafter, about 15 g of the acidic halogen solution is sprayed onto 50g of Comparative Sample A over a period of about 5 minutes whileComparative Sample A is fluidized in a mixing vessel. After anadditional 5 minutes of mixing, the sorbent composition is dried atabout 150° C. until a moisture level of about 8% is attained. Thebromine concentration on Sample E is measured to be about 5.4 wt. %.

Example 6

Sample F in accordance with the present disclosure is prepared in thefollowing manner. Sodium bromide is dissolved in DI water to form asodium bromide solution. 85 wt. % phosphoric acid is slowly added to thesodium bromide solution with stirring. The resulting acidic halogensolution contains about 27.8 wt. % Br and has a phosphoric acid tosodium bromide molar ratio of about 1:2. Thereafter, about 10.2 g of theacidic halogen solution is sprayed onto about 50 g of Comparative SampleA over a period of about 5 minutes while Comparative Sample A isfluidized in a mixing vessel. After an additional 5 min of mixing, thesorbent composition is dried at about 150° C. until a moisture level ofabout 8% is attained. The bromine concentration on Sample F is measuredto be about 5 wt. %.

Example 7

Sample G in accordance with the present disclosure is prepared in thefollowing manner. Ammonium bromide is dissolved in DI water. 85 wt. %phosphoric acid is slowly added to this ammonium bromide solution withstirring. The resulting acidic halogen solution contains 27.1 wt. %bromine and has a phosphoric acid to ammonium bromide molar ratio ofabout 1:2.25. Thereafter, about 11 g of the acidic halogen solution issprayed onto about 50 g of Comparative Sample A over a period of about 5minutes while Comparative Sample A is fluidized in a mixing vessel.After an additional ˜5 minutes of mixing, the sorbent composition isdried at about 150° C. until a moisture level of about 8% is attained.The bromine concentration on Sample G is measured to be about 5.3 wt. %.

Example 8

Sample H in accordance with the present disclosure is prepared in thefollowing manner. Sodium bromide is dissolved in DI water to form asodium bromide solution. 85 wt. % phosphoric acid is slowly added to thesodium bromide solution with stirring. The resulting acidic halogensolution contains about 30.8 wt. % Br and has a phosphoric acid tosodium bromide molar ratio of about 1:4. About 9.2 g of this acidichalogen solution is sprayed onto about 50 g of Comparative Sample A overa period of about 5 minutes while Comparative Sample A is fluidized in amixing vessel. After an additional ˜5 min of mixing, the sorbentcomposition is dried at about 150° C. until a moisture level of about 8%is attained. The bromine concentration on Sample H is measured to beabout 5 wt. %.

Example 9

Sample I in accordance with the present disclosure is prepared in thefollowing manner. Sodium bromide is dissolved in DI water to form asodium bromide solution. 50 vol. % sulfuric acid (H₂SO₄) is added to thesodium bromide solution slowly with stirring. The resulting acidichalogen solution contains about 21 wt. % bromine and has a sulfuric acidto sodium bromide molar ratio of about 1:1. About 17.7 g of this acidichalogen solution is sprayed onto about 50 g of Comparative Sample A overa period of about 5 minutes while Comparative Sample A is fluidized in amixing vessel. After an additional ˜5 minutes of mixing, the sorbentcomposition is dried at about 150° C. until a moisture level of about 8%is attained. The bromine concentration on Sample I is measured to beabout 6.3 wt. %.

Example 10

Sample J in accordance with the present disclosure is prepared in thefollowing manner. Ammonium bromide is dissolved in DI water to form anammonium bromide solution. 50 vol. % sulfuric acid is slowly added tothe ammonium bromide solution with stirring. The resulting acidichalogen solution contains about 19.4 wt. % bromine and has a sulfuricacid to ammonium bromide molar ratio of about 1:1. About 30 g of thisacidic halogen solution is sprayed onto about 50 g of Comparative SampleA over a period of about 5 minutes while Comparative Sample A isfluidized in a mixing vessel. After an additional ˜5 minutes of mixing,the sorbent composition is dried at about 150° C. until a moisture levelof about 8% is attained. The bromine concentration on Sample J ismeasured to be about 10.2 wt. %.

The ability to capture mercury may be measured by a dynamic mercuryindex (DMI) test developed by ADA Carbon Solutions, LLC and thatmeasures mercury (Hg) captured in micro-grams of Hg per gram of sorbentcomposition (pg Hg/g sorbent composition) in a flowing mercury-laden gasstream at elevated temperatures. An increase in, or higher DMI, or μgHg/g carbon (μg/g) captured, is an indication of a higher mercurycapture efficiency of a sorbent. The DMI test simulates conditions in acoal burning facility's flue gas stream. The test system includes apreheater, sorbent feed, mercury feed, and reaction chamber. The mercuryis fed into a reactor chamber along with the sorbent composition,wherein they are entrained. Uncaptured mercury is analyzed and DMIcalculated. Temperature of the entrained mercury and sorbent is kept atabout 325° F. (163° C.). Air entrainment and injection rates of betweenabout 1 and about 5 lb./MMacf (pounds sorbent per one million actualcubic feet) are maintained such that residence time of the sorbent inthe reaction chamber is about one second to simulate electricalgeneration unit (EGU) facility conditions. The mercury concentration inthe system is approximately 10 μg/m³.

Each of Samples A-J is measured to determine its DMI, and the resultsare listed in Table I.

TABLE I Mercury Capture Performance DMI Halogen (ug Hg/g Sample HalogenTreatment sorbent) Comparative Sample A None N/A 20 Comparative Sample B5.6 wt. % Br Conventional 308 from NaBr Comparative Sample C 5.1 wt. %Br Conventional 413 from NH₄Br Sample D 5.3 wt. % Br Acidic Solution 575from NaBr (H₃PO₄) Sample E 5.4 wt. % Br Acidic Solution 588 from NH₄Br(H₃PO₄) Sample F 5.0 wt. % Br Acidic Solution 464 from NaBr (H₃PO₄)Sample G 5.3 wt. % Br Acidic Solution 683 from NH₄Br (H₃PO₄) Sample H5.0 wt. % Br Acidic Solution 433 from NaBr (H₃PO₄) Sample I 6.3 wt. % BrAcidic Solution 486 from NaBr (H₂SO₄) Sample J 10.2 wt. % Br AcidicSolution 424 from NH₄Br (H₂SO₄)

The performance of a sorbent composition prepared from an acid-treatedhalide salt solution is found to be at least 25% to 50% higher in termsof overall mercury sequestration compared to a composition consisting ofthe same source and concentration of halide salt applied to the samebase sorbent without the benefit of acid pre-treatment.

Example 11

A prior art brominated PAC sorbent composition is compared to sorbentcompositions in accordance with the present disclosure by evaluating thesamples using x-ray diffraction (XRD). Sample K is formed by sprayingabout 50 g of Comparative Sample A with about 25.5 g of an acidichalogen solution comprising phosphoric acid and sodium bromide in amolar ratio of about 1:1 (acid to sodium bromide). The acidic halogensolution is sprayed onto Comparative Sample A while Comparative Sample Ais fluidized in a mixer. The resulting sorbent composition is then driedat about 150° C. for about two hours.

Comparative Sample L is made by a prior art process of spraying a sodiumbromide solution onto about 50 g of Comparative Sample A. This isachieved by spraying the sodium bromide solution onto Comparative SampleA while Comparative Sample A is fluidized in a mixer. The resultingcomposition is then dried at about 150° C. for about two hours. Thebromide content of the samples is measured to be about 10.8 wt. % forSample K and about 11.9 wt. % for Comparative Sample L.

Sample K and Sample L are analyzed by XRD to detect the presence ofcrystalline sodium bromide on the solid PAC sorbent. FIG. 2 shows theXRD spectra of both Sample K and Sample L. The presence of crystallinesodium bromide in Comparative Sample L is apparent from the number ofsharp peaks that indicate the presence of crystalline sodium bromide. Bycomparison, crystalline sodium bromide peaks are substantially absent inthe XRD spectrum of Sample K, indicating that the halogen species in theSample K sorbent composition, resulting from an acidic halogen solutionof an acid and a halogen species derived from a halide salt, is in asubstantially non-crystalline (e.g., amorphous) form.

Example 12

To further demonstrate the advantages of the sorbent compositionsdisclosed herein, water leachability tests are performed and the degreeof halogen (e.g., bromine) leaching is measured. For a leachabilitytest, Sample K and Comparative Sample L are dried at about 150° C. forabout 2 hours. Comparative Sample L is a conventionally brominated PACthat is produced in a manner similar to that described above withrespect to Comparative Sample B. About 10 g of each dried sample is thenslurried in about 250 ml DI water, and stirred at about 200 rpm forabout 1 hour. The two samples are then filtered from the aqueous slurryand dried at about 150° C. for about 2 hours. X-Ray Fluorescence (XRF)is conducted on both samples to measure the pre-leaching andpost-leaching bromine concentrations. The data is summarized in TableII.

TABLE II Sorbent Leaching Tests Pre-Leach Post-Leach Sample BrConcentration Br Concentration Br Loss % Comparative Sample L 11.92 wt.% 0.92 wt. % 92 Sample K 10.79 wt. % 3.75 wt. % 65

Sample K shows significantly less bromine loss due to leaching ascompared to Comparative Sample L. While not wishing to be bound by anytheory, these results indicate that the halogen species (e.g., Br) inthe two samples is attached to the underlying solid sorbent viadifferent mechanisms. These results indicate that the halogen species inComparative Sample L (e.g., NaBr crystallites) may be water soluble andreadily leached from the sorbent, whereas the halogen species in SampleK (e.g., an amorphous form of Br) may be more strongly bound orotherwise more permanently associated with the solid sorbent surface andtherefore not as susceptible to leaching. Leaching of the halogen fromthe sorbent may be a concern, particularly when the sorbent is collectedfrom the flue gas stream with fly ash.

Example 13

To demonstrate the efficacy of using iodine as an acid-activated halogenspecies, several samples are prepared that include iodine, either aloneor in combination with bromine.

For the preparation of these samples, a solution is formed comprisingabout 37.2 wt. % potassium iodide (28.4 wt. % iodine), about 21.8 wt. %phosphoric acid, and about 41 wt. % deionized water. The solutionincludes potassium iodide and phosphoric acid in about a 1:1 molar ratioand has a pH of about −0.55 and analysis shows that the solutioncomprises HI with a small amount of I₂. This solution is sprayed ontoComparative Sample A while Comparative Sample A is fluidized in a mixingvessel. The sorbent composition is dried at about 150° C. to reduce themoisture level. Three samples are prepared having iodine concentrationsof about 1 wt. %, 2 wt. %, 3 wt. % and 5 wt. %. X-ray diffractionanalysis shows no detectable presence of crystalline iodide forms on thecarbon.

DMI test as described above are performed and the results aregraphically illustrated in FIG. 3 (triangular data points). As is seenin FIG. 3, even at the very low concentration of 1 wt. % iodine, almost600 ug Hg/g sorbent is captured. Increasing the concentration to 2 wt. %or 3 wt. % increases the efficacy of the sorbent to about 950 to about1000 ug Hg/g sorbent. Also represented in FIG. 3 are two samples(circular data points) where a brominated PAC with about 5 wt. % Br issimilarly treated with 1 wt. % iodine and 2 wt. % iodine. The samplewith 1 wt. % iodine showed a DMI value of just over 600 ug Hg/g sorbent,and the sample with 2 wt. % iodine showed a DMI value of about 800 ugHg/g sorbent.

While various embodiments of a sorbent composition, a method for makinga sorbent composition and a method of using a sorbent composition havebeen described in detail, it is apparent that modifications andadaptations of those embodiments will occur to those skilled in the art.However, is to be expressly understood that such modifications andadaptations are within the spirit and scope of the present disclosure.

What is claimed is:
 1. A method for the treatment of a flue gas streamto remove contaminants from the flue gas stream, comprising the stepsof: combusting a fuel, the combusting of the fuel generating a flue gasstream comprising at least one contaminant contained in the flue gasstream; contacting the flue gas stream with a solid sorbent composition,wherein the contacting oxidizes at least a portion of the at least onecontaminant to form an oxidized contaminant; and after the contactingstep, separating the solid sorbent composition from the flue gas stream,wherein the solid sorbent composition comprises a solid sorbent and ahalogen species associated with the solid sorbent, wherein the halogenspecies is in a substantially amorphous form on the solid sorbent, andwherein the solid sorbent sequesters the oxidized contaminant.
 2. Themethod recited in claim 1, wherein the halogen species is formed bycontacting at least a first halide salt with an acid.
 3. The methodrecited in claim 2, wherein the halogen species associated with thesolid sorbent is dispersed within the acid.
 4. The method recited inclaim 1, wherein the acid is a mineral acid.
 5. The method recited inclaim 4, wherein the mineral acid is selected from the group consistingof sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid andcombinations thereof.
 6. The method recited in claim 5, wherein thesorbent composition comprises a conjugate salt of the mineral acid. 7.The method recited in claim 6, wherein the sorbent composition comprisesan anion selected from the group consisting of sulfate, bisulfate,phosphate, hydrogen phosphate, dihydrogen phosphate, nitrate, chloride,and combinations thereof.
 8. The method recited in claim 4, wherein themineral acid comprises sulfuric acid.
 9. The method recited in claim 8,wherein the sorbent composition comprises a polyatomic anion selectedfrom the group consisting of sulfate, bisulfate and combinationsthereof.
 10. The method recited in claim 4, wherein the mineral acidcomprises phosphoric acid.
 11. The method recited in claim 10, whereinthe sorbent composition comprises a polyatomic anion selected from thegroup consisting of phosphate, hydrogen phosphate, dihydrogen phosphateand combinations thereof.
 12. The method recited in claim 1, wherein thehalogen species is selected from the group consisting of bromine,chlorine, iodine and combinations thereof.
 13. The method recited inclaim 1, wherein the first halide salt comprises a halogen anion and acation selected from the group consisting of lithium, sodium, potassium,calcium, magnesium, ammonium, alkyl ammonium, hydrogen and combinationsthereof.
 14. The method recited in claim 13, wherein the halogen speciescomprises bromine.
 15. The method recited in claim 14, wherein thehalide salt is selected from the group consisting of sodium bromide,ammonium bromide and combinations thereof.
 16. The method recited inclaim 1, wherein the sorbent composition comprises at least about 0.5wt. % of the halogen species.
 17. The method recited in claim 1, whereinsorbent composition comprises at least about 5 wt. % of the halogenspecies.
 18. The method recited in claim 1, wherein the sorbentcomposition comprises not greater than about 30 wt. % of the halogenspecies.
 19. The method recited in claim 1, wherein the sorbentcomposition comprises not greater than about 15 wt. % of the halogenspecies.
 20. The method recited in claim 1, wherein the sorbentcomposition comprises at least about 3 wt. % moisture.
 21. The methodrecited in claim 1, wherein the sorbent composition comprises at leastabout 8 wt. % moisture.
 22. The method recited in claim 1, wherein thesorbent composition comprises not greater than about 15 wt. % moisture.23. The method recited in claim 1, wherein the solid sorbent is selectedfrom the group consisting of aluminas, silicas, silicates, carbonaceousmaterials, and combinations thereof.
 24. The method recited in claim 23,wherein the solid sorbent comprises a carbonaceous material.
 25. Themethod recited in claim 24, wherein the carbonaceous material is derivedfrom coal.
 26. The method recited in claim 25, wherein the carbonaceousmaterial is derived from lignite coal.
 27. The method recited in claim24, wherein the solid sorbent comprises powdered activated carbon. 28.The method recited in claim 27, wherein the solid sorbent has a medianaverage particle size (D50) of not greater than about 30 μm.
 29. Themethod recited in claim 28, wherein the solid sorbent has a medianaverage particle size (D50) of not greater than about 15 μm.
 30. Themethod recited in claim 1, wherein the solid sorbent has a total porevolume of at least about 0.2 cc/g.
 31. The method recited in claim 1,wherein the solid sorbent has a surface area of at least about 350 m²/g.32. The method recited in claim 1, wherein the sorbent compositionfurther comprises at least a second halogen species associated with thesolid sorbent.
 33. The method recited in claim 1, wherein the sorbentcomposition further comprises an acid gas agent.
 34. The method recitedin claim 33, wherein the acid gas agent is selected from the groupconsisting of aluminum hydroxide, zinc oxide, ammonium sulfate, ammoniumbisulfate, ammonium carbonate, ammonium bicarbonate, sodium carbonate,sodium bicarbonate, magnesium hydroxide, magnesium carbonate, magnesiumbicarbonate, urea, urea derivatives, metal hydroxides, ammoniumcompounds, and combinations thereof.
 35. The method recited in claim 33,wherein the acid gas agent comprises aluminum hydroxide.
 36. The methodrecited in claim 33, wherein the sorbent composition comprises at leastabout 1 wt. % of the acid gas agent and not greater than about 20 wt. %of the acid gas agent.
 37. The method recited in claim 1, wherein thesorbent composition further comprises a flow aid.
 38. The method recitedin claim 37, wherein the flow aid is selected from the group consistingof graphite, mica, talc, silica, stearates, clays, diatomaceous earthand combinations thereof.
 39. The method recited in claim 38, whereinthe flow aid comprises graphite.
 40. The method recited in claim 38,wherein the flow aid comprises mica.
 41. The method recited in claim 1,wherein the at least one contaminant is mercury.